The following discussion of the prior art is provided to place the invention in an appropriate technical context and enable the advantages of it to be more fully understood. It should be appreciated, however, that any discussion of the prior art throughout the specification should not be considered as an express or implied admission that such prior art is widely known or forms part of common general knowledge in the field.
The prior art discloses various methods to mark substrates. For example, it is known to use ink-jet printing methods to apply visual indicia to, for example, a building product such as a sheet of fibre cement or a coated building product. The visual indicia can take many forms, such as to indicate the source of the product, or product specifications, or product barcodes, trademarks, or other descriptors, etc. It is also known to print other visual indicia for the convenience of the installer, such as measurement markings, measurement grids, nailing guides, etc. For example see U.S. Pat. No. 5,673,489, U.S. Pat. No. 5,842,280, U.S. Pat. No. 6,115,926 and U.S. Pat. No. 6,049,987 to Robell which disclose various printing methods for printing visual indicia on wallboards, including ink-jet printing, screen printing and pad printing. However, these printing processes are costly and difficult to use. For example the ink adds cost to the final product and, for example, the ink-jet printing heads require constant maintenance and can relatively easily break down during production. Further, it will be appreciated that the entire intended visual marking can be ruined if but one of the many ink-jet heads fails or becomes blocked during use, thereby causing the product to be “faulty”, even if the substrate is fit for purpose. Also, re-working a sheet having an applied marking which is faulty is clearly inconvenient and costly.
What is needed is a way to mark a coated substrate which is substantially cementitious in composition without the need for relatively expensive inks, and without using relatively delicate printing equipment.
It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the above-mentioned prior art, or to provide a useful alternative.